Bob Easton

Archive for November, 2008

One of the traditional milestones in boat building is having setup complete. That’s when the backbone components can be assembled on the strongback or building jig. It’s the point where basic structural work is done and planking begins.

Almost there … almost because this step needs some epoxy work and the shop is a bit too cool for that now. Maybe there will be a warmer day soon.

A sense of scale can be gained from noticing the try square resting below the first bulkhead. It’s easy to visualize the planking. Note the three flat facets on the bulkheads and the mid frame, and the three lines on the stems.

Those warped bulkheads have now been wrestled into flatness. After the legs were attached and then screwed to the strongback, they were still wapred. Using 4 clamps per station to force the edges into the proper alignment, I pilot drilled and screw attached the bottom. That straightened out the warping. It’s holding now. We’ll see how long that lasts.

The stems were rough cut on the bandsaw a long time ago and set aside. They needed bevels on the leading edges. That turned out to be very easily done with an ancient, but very sharp, Stanley spokeshave, about 15 minutes each.

The finicky work was getting them properly attached to the bottom. They need to be exactly aligned on the center lines, exactly positioned with the 1/8 inch ends of the bottom board, and fastened with two screws each. Holding the parts in the correct relationship while drilling pilot holes is critical. Here’s where the long workbench really shines. Clamp one stem in the face vise. Clamp the other stem to the apron way down at the other end of the bench. A holdfast does that just right. Position the bottom over the edge of the bench, properly aligned on the stems. Hold in place with a holdfast (and a bit of iron weight). Drill, apply bedding compound, and screw. Flip end for end and repeat.

A little bit about screw fastenings for boats… Silicone bronze screws are recommended because they are corrosion resistant, and because by calling them “Marine” fasteners, they can be sold for three times the expected price. They are moderately strong, but also brittle. They are intended to hold things together, not “bring things together.” They are not like drywall or deck screws where “keep on torquing” will often tightened misalinged parts into tight compliance. Try that with these, and the reward is a quiet snapping sound … and soothing words of your own choosing.

The best technique for using silicon bronze fasteners is to ensure the parts fit very well together, clamp the parts into their proper position, drill pilot holes, best done with “Fuller bits,” and then apply the screws. Relieve clamp tension and pronounce soothing words.

Repair ability is a desireable trait, and the best screw head for repeated use is simple slotted. All of the cross-point and internal wrenching designs are too easily munged, cammed, or otherwise made useless. Simple slots have worked for centuries and require fewer soothing words.

Lumber that is completely knot free is virtually non-existent. Thus, we have knots … and most of them are potential drain holes. If a knot has a dark ring around it, that dark stuff is dead bark that will eventually rot, leaving the center of the knot free to pop out. So, we knock them out, clean out the soft material, carve a plug, and glue it into the void. The end result is still a bit of wood surrounded by a dark ring, but it’s reassuring knowing that the dark ring is epoxy, not rotting bark.

This boat bottom needed 11 such repairs, 9 knots, a larger long soft spot, and a small void containing an expired beetle larva. All of these were done after reducing the thickness of the glued up bottom to the desired 9/16 inch.

After the repairs, the outline of the bottom was lofted from the table of offsets and cut out. That too was an adventure. I haven’t gotten around to purchasing a really good saw for that kind of cut, and didn’t want to manhandle it through the band saw (one man shop). Instead, I made up a saw using a piece snapped out of an old band saw blade that I drilled and fitted into a hacksaw frame. It worked so well that actual cutting time was probably very close to what it would have been with the band saw. Either way requires trimming down to the final line with a plane.

The best reason for this post is to rave about how well the long workbench works.

The Fiddlehead’s bottom is made of three pieces of edge joined cedar, finished to 9/16″ thick. The center board is 11 feet long. The edge boards are each 8 feet long, and everything fits easily on the long bench.

The front apron is especially helpful for jointing the edges. Each of the boards had one face surfaced as a flat reference surface. Then, they are clamped on the apron in the correct relationship and their edges jointed together. Jointing them together ensures their edge angles match. The quick set up on the apron makes it easy to release and flip the boards up onto the bench for test fitting, and then set back up for fine tuning. I found it surprisingly easy to get to a “sprung joint” that was tight on the ends and about 1/32″ open in the middle. One clamp in the center was enough to produce evenly distributed squeeze-out during glue up. About as close to perfection as one can get, and it took surprisingly little effort. Yet, I did actually use more than one clamp, just to be certain. The primary thing holding the bottom of the boat together is these edge to edge glue joints.

The shop temperature is near the minimum for West System epoxy, so I let it cure a full 24 hours before moving on to thickness planing. Two dogs, two holdfasts, and a couple of turns on the tail vise gets the piece set up for planing in about 10 seconds. Plane one side for a while. Flip it, and plane the other side. Rinse, lather, repeat until we get to 9/16″. The big ole heavy #7 is rank set for a moderate cut; reasonably good material removal with no tearout.

Now that the workbench is done, it’s back to the Fiddlhead. We left off with a stack of resawn cedar.

Harry wants the bulkheads made up by laminating 1/4 inch thick pieces, making each bulkhead a 1/2 inch thick two ply board. Back when I did this for the model, my first result was a pair of bulkheads that curled up like potato chips. Learning from that, I took a more cautious approach. I resawed only to 1/2 inch thickness, not all the way to 1/4. I then did the lamination in two stages, edge to edge first, and then face to face.

The shop is not normally heated, and this week was very cooperative with overnight lows that did not reduce the shop below the 60 degrees needed for West System epoxy. After laminating, I planed both rough boards to near-final thickness; quick work for the big #7 plane. The elipses for hatch openings were cut with a fiddly old coping saw that’s now headed for the trash. Finished with a cabinet maker’s rasp. Handling these, I now appreciate Harry’s intent. They are unbelievably light, much lighter than they would be if made from regular 1/2 inch plywood. The cross grain lamination adds strength over using raw cedar.

The round piece shown in one of the openings is part of a hatch cover, another clever device that Harry designed. Clever, but devilish to construct.

Update – Nov 11, 2008: In only a couple of days these bulkheads have acquired a warp. They didn’t turn into potato chips, but have about 3/32 inch of curl. I don’t like it, but will leave them as they are. It’s probably not enough to make the boat tend to the left.

Update – Nov 20, 2008: More curl. They’ll be potato chips soon! A pencil can be rolled under either of two raised corners. I really don’t want to rebuild these, and I want even less to substitute plywood. I wonder what would happen if they got a good overnight soaking and then dried out under weights. Then again, it probably doesn’t matter that they are warped. The critical edge, the bottom, is still straight.

My extra long “English” workbench is done. The plan came form Christopher Schwarz’s excellent “Workbenches from Design & Theory to Construction & Use.” I lengthened it to accommodate the longer workpieces commonly found in boat building. It is 12 feet long and 2 feet wide.

Although made of common construction lumber (aka rather ugly Douglas fir), and with a thin top compared to some cabinet builders benches, it ends up being rock solid. While contemplating extending the length, I asked Chris if he thought a third set of legs would be needed. He suggested they wouldn’t hurt and pointed out a photo in his book of a bench with three sets of legs. I took a cautious approach and made the center legs a fraction of an inch short. The last thing I wanted was a teeter-tottering bench. Well, there’s no teeter-totter, and not much we can do to make those legs touch the floor. Maybe if I plop my truck engine on the bench? This is what they invented wedges for, isn’t it!

The Gramercy holdfasts from “Tools for Wood Working” work very well. They do need a top thicker than what I used. So, like I did for the dogs, I added doubling blocks under the holdfast locations. They’re great tools at an attractive price.

All of the lumber dimensioning and most all of the fitting and construction was done with hand tools. The only things I used electrons for were:

My old $10 hand drill helped with the large holes for the lead screws for the vises. As an aside, this is an amazing drill. It was a “no name” metal bodied $9.95 special in the early 1960s. I’ve used it almost continuously since them for the usual DIY stuff. It has outlasted two cordless drills and shows no signs of giving up.

I used the band saw to nibble away the waste near the curved areas of both vise faces.

A semi-retired miniature lathe and some idle mahogany were used for the ends of the vise handles.

Building the bench offered a few really interesting techniques: the use of Miller dowels for fastening the top (no metal to catch a plane while flattening), the use of drawboring to really tighten up a mortise and tenon joint, and the use of a wedged tenon for the parallel guide at the bottom of the face vice. Each technique was easy to learn, thanks to well written instructions, and each produces very strong joints.

Two coats of boiled linseed oil provide enough finish to keep blood from soaking into the top. Don’t ask how I know that.